AR51

**AR51** was a Merck investigational liquid hexavalent pediatric combination vaccine formulation evaluated in Phase 2 infant studies. The AR51 (12, 10) formulation contained 12 micrograms of *Haemophilus influenzae* type b polyribosylribitol phosphate conjugated to tetanus toxoid and 10 micrograms of recombinant hepatitis B surface antigen, together with diphtheria toxoid, tetanus toxoid, five-component acellular pertussis vaccine, and inactivated poliovirus types 1, 2, and 3. It was administered intramuscularly to induce protective active immunity against diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B, and invasive *H. influenzae* type b disease. AR51 is distinct from the later PR5I/V419 formulation marketed as Vaxelis, which uses PRP-OMPC rather than the PRP-tetanus-toxoid Hib conjugate used in AR51. ([cdek.pharmacy.purdue.edu](https://cdek.pharmacy.purdue.edu/trial/NCT00551629/))

Brand names

Vaxelis

Other names

DTaP-IPV-Hib-HepB vaccine (AR51 formulation)hexavalent vaccine AR51